(ô-rŏj'ə-nē) The process of mountain formation, especially by folding and faulting of the Earth's crust and by plastic folding, metamorphism, and the intrusion of magmas in the lower parts of the lithosphere. Unlike epeirogeny, orogeny usually affects smaller regions and is associated with evidence of folding and faulting. The long chains of mountains often seen on the edges of continents form through orogeny.